Gas turbines are widely used in industrial and commercial operations. For example, industrial gas turbines typically include one or more combustors to generate power or thrust. A typical commercial gas turbine used to generate electrical power includes a compressor section at the front, a combustor section around the middle, and a turbine section at the rear. Ambient air enters a compressor as a working fluid, and the compressor progressively imparts kinetic energy to the working fluid to produce a compressed working fluid at a highly energized state. The compressed working fluid exits the compressor and flows to one or more combustors where it mixes with fuel and ignites in a combustion chamber to generate combustion gases having a high temperature and pressure. The combustion gases flow to a turbine where they expand to produce work. For example, expansion of the combustion gases in the turbine may rotate a shaft connected to a generator to produce electricity.
The combustion gases exiting the turbine include varying amounts of nitrogen oxides, carbon monoxide, unburned hydrocarbons, and other undesirable emissions, with the actual amount of each emission dependent on the combustor design and operating parameters. For example, a longer residence time of the fuel-air mixture in the combustors generally increases the nitrogen oxide levels, while a shorter residence time of the fuel-air mixture in the combustors generally increases the carbon monoxide and unburned hydrocarbon levels. Similarly, higher combustion gas temperatures associated with higher power operations generally increase the nitrogen oxide levels, while lower combustion gas temperatures associated with lower fuel-air mixtures and/or turndown operations generally increase the carbon monoxide and unburned hydrocarbon levels.
In a particular combustor design, one or more late lean injectors, passages, or tubes may be circumferentially arranged around the combustion chamber downstream from the fuel nozzles. A portion of the compressed working fluid exiting the compressor may be diverted to flow through the injectors to mix with fuel to produce a lean fuel-air mixture. The lean fuel-air mixture may then flow into the combustion chamber where it ignites to raise the combustion gas temperature and increase the thermodynamic efficiency of the combustor. In another approach to increasing efficiency, fuel may be injected through a first stage of stationary vanes or nozzles located in the turbine section, as described in U.S. Pat. No. 7,603,863, assigned to the same assignee as the present invention. The injected fuel may cool the surface of the stationary nozzles before igniting to raise the combustion gas temperature flowing through the turbine section.
Although injecting fuel through late lean injectors in the combustor section and/or stationary nozzles in the turbine section effectively increases efficiency without producing a corresponding increase in undesirable emissions, continued improvements in systems and methods of supplying fuel in a gas turbine would be useful.